1. Field of the Invention
The present invention relates to a ceramic heater provided with a heater body formed of ceramics on which an object of processing is placed for heat treatment and a cooling module including plate-shaped structure for cooling the heater body, as well as to a semiconductor manufacturing apparatus having the ceramic heater mounted thereon.
2. Description of the Background Art
Conventionally, in the process of manufacturing a semiconductor, a semiconductor substrate (wafer) as an object of processing is subjected to various processes including film formation and etching. In a semiconductor manufacturing apparatus used for performing such processes on the semiconductor substrate, a ceramic heater is used for holding and heating the semiconductor substrate.
By way of example, in the photolithography process, a resist film pattern is formed on a wafer. In this process, steps of washing the wafer, heating and drying, cooling, thereafter applying a resist film on the wafer surface, placing the wafer on a ceramic heater in a photolithography processing apparatus, drying, and thereafter exposure and development are performed. In the photolithography process, temperature at the time of drying the resist has significant influence on the quality of the applied film, and therefore, uniformity of the temperature of ceramic heater during processing is important.
Further, for improving throughput, these process steps on the wafer must be finished in as short a time as possible. Therefore, the inventors of the present invention have proposed semiconductor manufacturing apparatuses having cooling means capable of cooling the heated heater in a short period of time. By way of example, Japanese Patent Laying-Open No. 2004-014655 proposes a semiconductor manufacturing apparatus including a plate-shaped structure that can be brought into contact with and separated from a surface opposite to the wafer-mounting surface of the heater. Japanese Patent Laying-Open No. 2005-150506 proposes a semiconductor manufacturing apparatus in which a passage for a cooling liquid is formed in the plate-shaped structure so that cooling rate is further increased and uniformity in temperature distribution of the heater can be maintained from the start to the end of cooling.
In the process of manufacturing semiconductors including recent electronic devices, higher uniformity of temperature distribution of the heater has been required. Higher uniformity of heater temperature distribution is required from the start to the end of cooling, not to mention during heating and holding at the heated temperature. Further, increase in the rate of temperature increase and the rate of cooling is also required.
Recent semiconductors come to have thinner interconnections, and accordingly, KrF or ArF has come to be used as a light source for exposure in the photolithography process, and a chemical amplification film is used as the resist film. In this process, acid generated at the time of exposure serves as a catalyst, so that the resist film is made soluble in the following step of development, that is, the film can be washed away. In the photolithography process, strict control of temperature variation is necessary, for example, in the step of PBA (Post Applied Baking) in which the resist film is spin-coated and thereafter a solvent is evaporated before exposure to increase viscosity and to prevent flow during exposure, and in the step of PEB (Post Exposure Baking) in which the resist film is cured after exposure.
It is often the case that the heater temperature is changed for processing in these PAB and PEB steps. For instance, after processing at 180° C., the heater temperature may be lowered by 50° C. for processing at 130° C. In such a case, it has been required to attain uniform heater temperature distribution as soon as possible after the start of cooling, in order to increase throughput.
In the conventional semiconductor manufacturing apparatus described above, a cooling module has been proposed in which a passage 15 for circulating a cooling liquid is formed in a plate-shaped structure 14, so that the cooling rate is further improved and the uniformity of heater temperature can be maintained from the start to the end of cooling, as shown, for example, in FIG. 7. The apparatus, however, becomes expensive as passage 15 must be fabricated through machine processing, and the apparatus cannot be provided at a low cost. Further, dependent on the material of plate-shaped structure 14, the structure may be corroded by the fluid, possibly causing leakage of the fluid, and therefore, it is not very reliable and use for a long period has been difficult. When a material highly resistant to corrosion is used for plate-shaped structure 14, it becomes prohibitively expensive.